From what you have written, I understood that Lady’s husband died and now her mother-in-law wants share in her husband’s property.
If she is governed under the Hindu Succession Act then under Section 8, her husband’s property will be inherited by her daughter, her, and her mother-in-law.
Her mother- in law does have a right in her husband’s property. Then afterward, if she (mother-in-law) didn’t execute a will and died intestate (without a will), her property will be inherited by her sons, daughters, and the lady’s children.
Hope this helps